The invention relates to measuring and testing devices, but more particularly, the invention relates to a tool for measuring rotor or wheel imbalance.
Wheel balancing tools of the hanging type are used to determine the static imbalance of a wheel or rotor. Operation of the tool requires that the center of gravity of the article being balanced be placed below a flexible suspension point of the tool. When the center of gravity of the article being balanced does not coincide with the axis of the suspension cable, the offset center of gravity causes an angular tilting of the article in relation to the suspending cable. The degree of imbalanced may be indicated by means of an annular disc attached to the cable and a juxtaposed indicator plate attached to the article.
Sensitivity of such suspension balancing devices is influenced by the displaced location of the center of gravity of the article being tested below the suspension point of the tool, and by the ease and accuracy of determining measured angular deflections between the suspension cable and suspended article.
Adjustment of the center of gravity location may be made by moving threaded wheel adapters along a threaded tube. An example of such a method is shown in U.S. Pat. No. 2,698,537 (FIG. 5). The problem with such a means for adjustment is that the article being balanced must be repetitively disengaged from the adapters as the adjustment for center of gravity location is made. The balanced article may be quite heavy which could lead to a tedious operation as the article is disengaged from the tool and the adapters adjusted.
Once the center of gravity is properly located in relation to the balancing tool, it becomes important to accurately read the degree of imbalance such as with discs and indicator plates. Examples of annular discs attached to a suspension cable and a reference plate attached to the article being balanced is shown in U.S. Pat. Nos. 2,481,256 (FIG. 6) and 2,647,398 (FIG. 4). The problem with such indicators is that it is very difficult to view very small angular displacements measured by the disc and reference plate as the article being balanced approaches a true, static balance. An observer must attempt a line of sight as close to the suspending cable as possible for an accurate reading.